A short salt synopsis

Prepared Foods, March, 1998 by Claudia D. O'Donnell

Through its ability to alter the osmotic pressure of water, it "dehydrates" curd proteins during cheese manufacturing and helps slow microbial spoilage and increase the safety of hams and olives. In sausage processing, it extracts proteins that then bind the meat. Salt provides the taste punch behind popcorn and rounds out the flavor in vanilla pudding.

Salt's physiological impact is still being researched. Its ability to suppress or enhance other tastes, for example, partly depends on the concentration of the compounds involved. On the nutritional front, high sodium intake levels increase hypertension in a minority of U.S. consumers. However, very low levels of sodium appear to do the same. (See PF, July 1997, page 48 and sidebar.)

Considering the variety of uses of salt, choosing the optimum salt among dozens of available grades can be a challenge.

Properties via Processing

Salt processing methods can be roughly grouped into three categories: direct mining, solar evaporation of natural brines and mechanical evaporation of artificial brines (either solution-mined from underground salt deposits or prepared by redissolving crystalline salt). Mechanical evaporation may occur in vacuum or in open-pan crystallizers.

In direct processing, rock salt is mined from sub-surface deposits. Size-reduction equipment grinds the mined salt down to desired dimensions. Smooth, planar-surfaced crystals result. This salt is primarily used in surface applications such as coatings on pretzels.

Solar processing utilizes sun and wind energy to evaporate the water from seawater or natural brines in shallow holding ponds to produce "solar salt." "This process may take several years to complete and is carefully managed to separate salt from other minerals. Subsequent washing and drying results in an 'all natural' sea salt," says Skip Niman, director of quality administration for a salt supplier.

"Most food-grade salt used today is produced through vacuum crystallization of a purified, saturated brine," says David Strietelmeier, technical director with a salt supplier. This produces concentric or cube-shaped, relatively dense salt crystals. Dendritic salt, which is a porous, less dense crystal, is produced by the addition of trace amounts of YPS (yellow prussiate of soda or sodium ferrocyanide) to the brine. "By compacting vacuum-granulated salt into thin platelets, coarse grades of flake salt can be created," he adds.

The Alberger process also involves mechanical evaporation, but unlike the vacuum process, it occurs in an open evaporating pan using steam energy. "The end product is a unique, three-dimensional flake salt of extremely light bulk density," says Niman.

Additional processing steps such as grinding, screening, or addition of other additives create a plethora of salt forms that differ in purity, bulk density, form and particle size distribution. These characteristics impact solubility, "blendability," adherence, friability, flowability and resistance to caking. These factors determine a salt's suitability in various applications. Two typical examples follow.

* Topical uses

Nowhere is the appearance of salt more important than when it is visible in or on a product. "A 14 to 20 mesh rock salt is the most popular for pretzels," says Strietelmeier. Here, rock salt's hardness is useful since a large percentage falls off in pretzel operations and is subjected to rough handling during recycling.

Adherence is also critical in snacks and crackers. A lighter bulk density, finer particle size, flaked shape for greater surface contact and the presence of surface oil on the product all increase adherence. These are general rules of thumb, however. On saltines, a fine grade will dissolve too rapidly on the surface and produce a strong surface brine that causes excessive spring, open blisters and brown spots. A coarser grind is also preferred for its appearance, says Strietelmeier.

The reduction of surface oil in lower fat snacks presents an additional challenge. Processors have turned to starch, dextrose and other carbohydrate-based systems to help keep the salt on the product.

Uniformity of size is another important salt characteristic. It improves both the ease of application and the appearance of a topical salt.

* Dry mixes.

In seasoning blends, dry soup and cake mixes, ingredients may tend to settle out (stratify) during mixing, transportation and filling operations. "Matching the salt particle size and density to that of the major component in a dry blend is the most important step to prevent ingredient separation," says Niman.

Insoluble anticaking agents that improve salt flowability may also increase dusting. These agents include tricalcium phosphate, magnesium carbonate, silicon dioxide and sodium silicoaluminate. "Dusting can be reduced through the addition of glycerine, propylene glycol or polyethylene glycol," says Niman.

If the end product needs to be water soluble, soluble conditioners such as propylene glycol, glycerine, ferric ammonium citrate or YPS can be added to the salt (or any dry blend), Niman points out. It should be noted that if free iron is present in the finished product, especially in lower pH foods, the YPS may react to form prussian blue.